(1) Field of the Invention
The present invention relates to a method for refining sugar solutions. More particularly, the present invention relates to a method for refining sugar solutions with magnesia in which the used magnesia is calcined and used repeatedly.
(2) Description of the Prior Art
Various methods have heretofore been proposed for refining cane juices, beet juices, liquors molasses and syrups obtained from cane, beet and raw sugar and other sugar solutions comprising sucrose as the main component.
Refining methods mainly adopted in the sugar refining process are a carbon dioxide saturation method (carbonation method), a phosphoration method, a bone black or active carbon method, an ion exchange resin method and combinations of these methods.
In the case of the carbon dioxide saturation method, since kinds of thermal energies used in sugar refining plants are expected to be increased according to location conditions of the plants, there are risks of reduction of the CO.sub.2 content and incorporation of harmful substances owing to changes of compositions of chimney gases, and in a special case, it will happen that steam per se is purchased and no chimney gas is formed.
Furthermore, in order to effectively saturate a sugar solution with CO.sub.2, it is necessary to control the concentration of the sugar solution below a certain critical level, and therefore, the carbon dioxide saturation method is defective in that a relatively large quantity of energy is necessary for concentration of the sugar solution.
Moreover, in the carbon dioxide saturation method, since a large quantity of lime is used, the amount of the waste cake produced is increased, disposal of the waste cake is troublesome and a problem arises in connection with prevention of environmental pollution.
The phosphoration method is defective in that since control of the reaction is difficult, decomposition of sucrose is readily caused, and that filtration of the refined sugar solution is troublesome and phosphoric acid is expensive.
The bone black method is defective in that expensive bone black should be used in large quantities and installation costs are increased.
The active carbon method is defective in that powdered active carbon is expensive. Besides, today it has grown to be difficult to obtain active carbons of a high quality due to shortage of natural resources.
The ion exchange resin method is defective in that if a sugar solution containing large quantities of impurities is passed through a column packed with an ion exchange resin without any appropriate preliminary treatment, sufficient refining of the sugar solution is not accomplished, and furthermore, this method involves such problems as insufficient passage of the sugar solution and degradation of the ion exchange resin.